If it was working fine before, get a can of compressed air. With the laptop off, aim it into the fan outlet and give it a good blast. That'll blow most of the dust off the heat sink and fan, and improve its cooling again. Sometimes, after a few months of use, that's the main cause of overheating problems.
If you can't get cans of compressed air, try an auto shop with an air compressor for filling tires. That'll generate enough air pressure to give a good blast.